The present invention relates to a drilling device used in particular for the drilling of holes intended for the extraction of rocks and ores, in which a rotary movement is imparted to the drilling tool, this assembly being mounted on an advancing device which enables a thrust to be exerted on the tool during drilling.
It is known that the torque created by the contact of the tool or drilling head with the ground increases with the thrust applied.
It is therefore necessary to provide regulating devices enabling the thrust exerted on the tool to be adapted to the maximum torque admissible by the drive device, in order to protect the tool from risks of jamming in the drilled ground.
FIGS. 1 and 2 represent, very schematically, a rotary percussion drilling device of known type, in two operating positions. These figures show a hammer drill 1 equipped with a tool 2 associated on the one hand with an impact device 3 and on the other hand with a rotary drive device 4. The hammer drill is mounted to be displaceable relative to the ground 5 in which a bore is to be made with the aid of an advancing system 6 mounted on a slideway 7. The advancing system comprises a hydraulic ram 8 whose body is solidly fixed to the device 6 and whose column 9 bears on a fixed point. The various movements are obtained from a hydraulic pump 10 which feeds, via three distributors, 12, 13 and 14 respectively, the impact device 3, a hydraulic motor 15 and the ram 8. The connections are embodied by way of a series of hoses, 16, 17 and 18 respectively. The feed circuit of the hydraulic motor for driving the tool in rotation comprises the hoses between the hydraulic pump 10 and the distributor 13, the distributor 13, the hose 17a, the rotary motor 15, the return hose 17b and the hose between the distributor 13 and the return to atmosphere. A circuit reversing device 19 is placed in the circuit situated between the distributor 14 and the ram 8 for advancing the drilling device. The reversing system 19 is controlled by the pressure of rotation of the motor 15, ensuring the rotational drive of the drill. The maximum admissible rotational pressure at which the reversing system reacts is adjustable. The information pick-up of this system is, nevertheless, very distant from the inlet of the motor 15, for reasons of bulk, which results in very substantial hose lengths.
Below the maximum admissible rotational pressure, the fluid feed of the various motor members takes place, as shown in FIG. 1, via the hoses shown in solid lines. The reversing system 19 is in its position of rest and does not act on the advancing circuit. In the event that the tool 2 becomes jammed in the ground, the rotational pressure increases. If the pressure exceeds a predetermined value, set on the reversing system 19, the latter reverses the feed direction of the ram 8, as shown in FIG. 2, allowing the tool to move back.
In such a case, the hydraulic rotational pressure of the motor is not measured directly, and the drill is very remote from the control system. The measured pressure is the sum of the rotational pressure of the motor and the losses of line head within the circuit formed by the hose 17. However, the losses of head within a circuit are very variable as a function of temperature, which influences viscosity, and of the hydraulic fluid flow.
In order to work in all conditions, it is necessary to adjust the reversing switch device 19 to a value such that the maximum admissible rotational pressure is equal to the rotational pressure plus the maximum loss of head.
The rotational pressure due to mechanical torque being constant, the losses of head are for their part variable as a function of temperature. The measured pressure is therefore variable as a function of temperature. This type of device does not allow fine adjustment of the reversing system.